Bryan R. Morris, Senior R&D Engineer & Nastausha Hefner, Marketing Manager, STOCKMEIER Urethanes USA Inc.
STOCKMEIER Urethanes’ Stobielast® S polyurethane (PUR) coatings for recycled rubber are pre-pigmented and moisture cured. Utilizing only the highest UV-stable pigments and specialized dispersion processes, these materials provide high hiding-power at low consumptions with a variety of color options. As a commitment to our continued efforts towards sustainability, these products incorporate renewable, bio-based materials. Competitive technologies in the market are water-based polymers of varying chemistry and require special drying equipment to avoid streaking in the packaging and microbial attack during storage. In addition, many of the water-based materials offer poor abrasion resistance during processing which results in loss of coating during mixing and loss of color for the consumer. What are the process benefits of using pigmented PUR coatings? Reduction of inventory, more consistent color, ease of addition, cleanliness and efficiency of processing, and outstanding durability are key.
Polyurethane is more than a coating that dries on the rubber; PUR chemically crosslinks and encapsulates the rubber which makes it the product of choice for performance. There are three, principal methods for coloring rubber with polyurethane:
- The loose rubber is colored with solid pigments that are added during mixing. The solid pigments are then encapsulated with a clear, moisture-cure PUR. Solid pigments are high in cost and add additional complexity to the coloring process. In addition to having to add multiple pigments to achieve certain colors, some pigments require specialized wetting for full intensity. This often cannot be achieved by simple blending with the rubber and PUR and more pigment is required. Additionally, not all pigments are UV stable and may result in loss of color over time.
- The loose rubber is colored with a liquid pigment-dispersion and then encapsulated with a clear, moisture-cure PUR. Though far less prone to the issues described in process one, additional inventory and processing inconsistencies and times are still a factor for consideration
- The loose rubber is both colored and encapsulated with a pre-pigmented, moisture-cure, PUR coating. The polyurethane, stabilizers and pigments are all built into one product and excess inventory, inconsistent color and expensive drying equipment are eliminated! This has been the process of choice increasingly over the last decade as the full benefits have been realized.
STOCKMEIER Urethanes utilizes proprietary catalysts that snap cure the PUR coatings and eliminate the need for a heating tunnel or any other exterior drying tools.
The quality of the rubber feedstock, the mixer used for the coating process and proper agitation of the coating are critical factors for successfully coloring recycled rubber. Please contact your STOCKMEIER Urethanes representative for specific guidance.
“So, what’s the cool thing about this market?” asks Morris. “Before tires were recycled and utilized to make colored rubber for playgrounds and mulch (and a variety of other consumer goods), they would go straight into the dump. It is mind boggling to think that around 280 million tires are discarded each year by American motorists.1 Converting these tires to crumb and buffings allows for the tires, which were once garbage and an environmental concern, to be converted into commodities that created wealth and jobs. It doesn’t get much better than that! In the past, when we would give tours of our plant and lab, our guests were always amazed at this innovation. And why shouldn’t they be? This is something that we’re certainly proud to be a part of!”
Finding methods to mitigate the materials that go into landfills is critical to the health of our communities. While many things that make their way into the trash are biodegradable and decompose over time, tires certainly do not fall into this category. Tires are engineered to last. Their hollow and curved shape take up excessive space and cause them to settle unevenly and rise to the surface which in turn can harm landfill covers. Due to their chemical composition, tires are excellent retainers of heat. This retention of heat comes with the risk of ignition and, once tire rubber begins to burn, it is extremely difficult to extinguish. Flames from the burning of tires in large quantities can release dense and unhealthy smoke. STOCKMEIER Urethanes takes great pride in its goal to one day eliminate the disposal of tires into landfills. Turning waste into value and jobs is the smart solution!